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LIBRARY 

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University  of  California. 

RECEIVED    BY    EXCHANGE 


Class 


The  Electrolytic  Determination 
of  Manganese  and  Its  Sepa- 
ration from  Zinc  and  Iron. 


THESIS. 


Presented  to  the  Faculty  ot  the  Department 
of  Philosophy  ot  the  University  ot  Penn- 
sylvania in  Partial  Fulfilment  of  the 
Requirements  for  the  Degree  ot 
Doctor  of  Philosophy, 


BY 


George   Philipp  Scholl, 
Philadelphia. 


Eastox.  Pa.  : 

The  Chemical  Publishing  Company. 

1903. 


The  Electrolytic  Determination 
of  Manganese  and  Its  Sepa- 
ration from  Zinc  and  Iron, 


THESIS. 


Presented  to  the  Faculty  of  the  Department 
of  Philosophy  ot  the  University  of  Penn- 
sylvania in  Partial  Fulfilment  of  the 
Requirements  for  the  Degree  of 
Doctor  of  Philosophy, 


BY 


George   Philipp  Scholl, 

n 

Philadelphia. 


OF  THE     * 

UNIVERSITY 

OF 


Easton,  Pa.  : 

The  Chemical  Publishing  Company. 

1903. 


THE 


UNIVERSITY 


THE  ELECTROLYTIC  DETERMINATION  OF  MANGA- 
NESE AND  ITS  SEPARATION  FROM  ZINC  AND  IRON. 

The  deposition  of  manganese  during  electrolysis  takes  place  in 
a  different  manner  from  that  of  the  other  metals,  with  the  excep- 
tion of  lead,  inasmuch  as  under  ordinary  conditions  the  metal  is 
not  deposited  as  such  on  the  kathode,  but  comes  down  as  peroxide 
on  the  anode.  Under  certain  conditions  it  is,  however,  possible  to 
deposit  the  metal  as  such  on  the  kathode,1  but  its  quantitative  esti- 
mation has  been  found  impossible  on  account  of  the  very  rapid 
oxidation  of  the  metal  during  the  process  of  drying.  This  method 
therefore  cannot  be  used  for  analytical  purposes. 

The  deposition  of  manganese  as  peroxide  for  the  purpose  of  its 
quantitative  chemical  estimation  by  electrolysis  has  been  the  subject 
of  a  good  deal  of  investigation,2  but  the  results  have  not  been  very 
satisfactory.  The  stumbling  block  in  the  way  of  a  successful  pre- 
cipitation has  been  the  fact,  that  it  is  extremely  difficult  to  obtain 
the  deposit  on  the  anode  in  an  adherent  form,  it  showing  a  tend- 
ency to  become  loose  and  to  scale  off.  This  even  takes  place 
when  the  peroxide  is  deposited  on  a  platinum  dish,  the  inner  sur- 
face of  which  has  been  roughened  by  subjecting  it  to  the  action  of 
a  sand-blast.  Owing  to  this  tendency,  manganese  is  probably  the 
most  difficult  metal  to  deal  with,  as  far  as  electrolysis  is  concerned. 

Various  electrolytes  have  been  proposed  for  the  quantitative 
estimation  of  manganese  by  electrolysis,  but  in  1894  Classen3  states, 
that  none  of  the  methods  heretofore  proposed  had  been  found  by 
him  to  yield  satisfactory  results.  He  advises  the  use  of  acetic  acid 
as  an  electrolyte  and  states  that  it  has  been  found  by  him  to  be  the 
most  suitable  of  all  the  organic  acids.  This  statement  is  repeated 
in  the  last  (4th  edition)  of  his  "Quantitative  Chemical  Analysis  by 
Electrolysis,"  translated  by  Herrick  and  Boltwood,  1898,  p.  149, 
where  it  is  further  said,  that  "the  precipitation  of  large  quantities, 

1  Smith  and  Prankel :  Journal  Analyt.  Chem.,  3,  3S5;  Chemical  News,  60,  262. 

2  literature  given  by  Smith,  Electrochemical  Analysis,  3rd  ed.,  1902;  Riche  :  Annales 
de  Chimie  et  de  Physique  [5th  series],  13,  50S  ;  Iyuckow  :  Zeitsch.  f.  anal.  Chem.,  19,  17  ; 
Schucht;  Zeitsch.  f.  anal.  Chem.,  33,  493;  Classen  and  von  Reiss  :  Berichte  deutsch. 
Chem.  Ges.,  14,  1622  ;  Brant:  Zeitsch.  f.  anal.  Chem.,  38,  581;  Riidorff  ;  Zeitsch.  f.  angew. 
Chem.,  15,  6  ;  Classen :  Berichte  deutsch  chem.  Ges.,  37,  2060  ;  Engels  :  Zeitsch.  f.  Elec- 
trochemie,  3,  413;  3,  286;  Groeger:  Zeitsch.  f.  angew.  Chem.,  1895,  p.  253;  Koeppel:  Zeitsch. 
f.  anorgan.  Chem.,  16,  268. 

i  Berichte  d.  deutsch.  Chem.  Ges.,  37,  2060. 


173285 


even  when  roughened  dishes  are  used,  cannot  be  successfully  car- 
ried out,  since  it  is  impossible  to  obtain  firmly  adherent  precipi- 
tates." Evidently  no  improvement  in  this  method  had  been  made 
up  to  1901,  for  in  Classen's  large  handbook  on  "Selected  Methods 
of  Analytical  Chemistry,"  which  appeared  in  that  year,  the  follow- 
ing statement  is  found  on  page  368 :  "In  acetic  acid  solution  it  is 
only  possible  to  deposit  quantities  of  about  0.08  gram  of  manga- 
nese in  the  form  of  peroxide,  even  on  roughened  dishes." 

A  few  years  ago,  Engels1  proposed  a  method,  which  is  said  to 
give  firmly  adherent  deposits  up  to  0.25  gram  of  manganese,  and 
which  consisted  in  adding  chrome  alum  in  quantities  of  from  1.5 
to  2  grams  to  the  solution  of  manganese  sulphate.  This  method  is 
open  to  objection,  inasmuch  as  the  addition  of  chrome  alum  intro- 
duces a  complex  metallic  compound  into  the  electrolyte,  which 
compound  by  its  own  decomposition  under  the  influence  of  the  cur- 
rent may  give  rise  to  complications.  Further,  as  stated  by 
Kaeppel,2  an  extended  washing  of  the  deposit,  on  account  of  the 
chromic  acid  adhering  to  it,  is  absolutely  necessary,  and  a  source 
of  error  may  easily  be  introduced  from  the  fact,  that  chromic  acid, 
which  is  carried  down  by  the  deposit,  is  quite  firmly  held  by  the 
peroxide  of  maganese. 

The  last  work  done  on  the  subject  in  recent  years  has  been  by 
Kaeppel,  who  in  1898  published  a  method2  by  which,  according  to 
him,  very  adherent  deposits  of  manganese  peroxide  are  obtained. 
It  consists  in  the  addition  of  acetone,  in  quantities  varying  from 
2.5  to  10  cc,  to  a  solution  of  manganese  sulphate.  He  gives  one 
experiment,  in  which  he  obtained  1.61  grams  of  peroxide  of  man- 
ganese in  a  firmly  adherent  form.  Classen3  states,  however,  that 
the  carrying  out  of  Kaeppel's  method  in  his  laboratory  has  not  led 
to  any  satisfactory  result. 

The  question  of  the  deposition  of  manganese  was  therefore,  as 
is  apparent  from  the  above,  in  quite  an  unsatisfactory  state. 
Engels's  method  was  open  to  the  objections  mentioned,  and 
Kaeppel's  method  was  described  by  him  in  such  a  way  in  his  publi- 
cation, that  it  was  impossible  to  repeat  it.  As  has  been  justly 
criticized  by  Classen,4  he  omitted  to  state  the  precise  conditions, 
under  which  his  experiments  were  performed.     He  gives  no  data 

1  Zeitsch.  f.  Electrochemie,  2,  413  ;  3,  286. 
J  Zeitsch.  f.  anorgan.  Chemie.  16,  268. 

3  Selected  Methods  of  Analytical  Chemistry,  1901,  p.  370. 

4  Ausgewahlte  Methoden  der  analytischen  Chemie  (selected  methods,  etc.),  p.  370. 


whatever  in  regard  to  the  size  and  form  of  his  electrodes,  the  cur- 
rent density  at  the  anode  and  kathode  or  the  general  arrangement 
for  carrying  out  the  electrolysis.  It  is  quite  apparent  to  any  one 
conversant  with  electrolytic  operations  in  general,  that  these  are 
questions,  which  largely  influence  the  result,  and  on  which  the 
success  of  the  operation  may  depend  and  usually  does  depend  to  no 
small  degree.1  Such  being  the  case,  the  question  presented  itself, 
if  it  was  not  possible  to  find  another  electrolyte,  which  would  lend 
itself  to  a  more  satisfactory  deposition  of  the  peroxide  of  manga- 
nese, and  to  the  separation  of  manganese  from  other  metals,  prin- 
cipally iron.  Organc  acids  appeared  most  suitable  for  this  pur- 
pose. Classen2  maintains,  that  strong  inorganic  acids  interfere 
with  the  deposit  and  even  make  it  impossible.  The  same  author's 
statement,  that  acetic  acid  is  the  best  of  all  organic  acids,  has  been 
referred  to  above.  No  further  experimental  details  are  given  in 
his  publications  to  substantiate  that  statement  and  there  is  also  no 
mention  made  as  to  which  organic  acids  have  been  tried  and  under 
what  conditions.  Kaeppel,  in  his  paper,  makes  some  remarks 
about  formic  acid.  He  says:  "I  then  carried  out  experiments 
with  formic  acid.  By  the  use  of  a  few  drops  of  it,  an  adherent 
deposit  could  also  be  obtained,  but  it  was  shown  still  more,  that  a 
quantitative  deposition  could  not  be  effected.  The  addition  of 
more  than  5  drops  of  the  acid  prevented  the  deposition  of  peroxide 
altogether.  This  statement  is  also  unaccompanied  by  any  experi- 
mental evidence  as  to  the  strength  of  acid  used,  the  manner  of 
carrying  out  the  electrolysis  and  the  general  conditions  under 
which  it  took  place. 

The  above  statements  to  the  contrary  notwithstanding,  it  was 
considered,  that  formic  acid,  on  account  of  its  simple  constitution, 
would  be  an  extremely  desirable  substance  to  be  used  as  electro- 
lyte, and  it  was  thought,  that  under  the  right  conditions  it  might 
be  made  to  yield  satisfactory  results.  It  was  therefore  determined 
to  try  it  with  the  addition  of  sodium  formate. 

The  apparatus  used  for  carrying  out  the  experiments,  consisted 
of  the  usual  stand  for  electrolysis,  provided  with  a  glass  rod 
carrying  a  ring  wih  3  contact  points,  for  the  purpose  of  supporting 
the  platinum  dishes  in  which  the  deposition  took  place,  and  the 

1  See  in  this  connection  the  pertinent  remarks  of  Smith  :Electrochemical  Analysis 
3rd  ed.,  p.  33-36. 

2  Ibid.,  p.  368.    Quantitative  Analysis  by  Electrolysis,  p.  149. 


usual  clamp  for  fastening  the  other  electrode.  The  current  was 
supplied  by  storage  batteries,  which  were  constantly  kept  in  a 
charged  condition.  The  current  was  regulated  by  means  of  a  disk 
rheostat,  and  a  Weston  voltmeter  and  amperemeter  were  kept 
constantly  in  the  circuit.  The  platinum  dishes  used  for  the  deposi- 
tion of  the  peroxide  of  manganese  were  of  the  usual  shape  and 
had  a  diameter  of  9  cm.  Their  interior  surface  was  roughened. 
The  kathode  consisted  of  a  spiral  of  platinum  wire  of  1^2  mm. 
diameter,  having  a  surface  of  6  square  cm.  As  usual,  the  dishes 
were  covered  by  cover  glasses. 

A  solution  of  manganese  sulphate  was  made  up,  calculated  to 
contain  about  10.60  grams  of  manganese  in  the  liter.  The  formic 
acid  used  in  the  experiments  was  the  chemically-pure  article  of 
1.06  specific  gravity,  made  by  Merck  &  Co.  The  electrolysis  was 
conducted  in  the  following  manner:  10  cc.  of  the  manganese 
sulphate  solution  were  introduced  into  the  platinum  dish  and 
5  cc.  of  the  formic  acid  solution  of  1.06  specific  gravity  added  to  it. 
A  solution  of  .10  cc.  of  sodium  formate,  containing  1  gram  of  the 
salt,  was  then  added,  and  the  whole  volume  of  the  solution  made 
up  with  distilled  water  to  about  130  cc,  so  that  it  covered,  as 
accurately  as  could  be  determined,  100  sq.  cm.  of  the  surface  of 
the  dish.  The  dish  was  connected  as  anode  and  the  spiral  kathode 
introduced  into  the  solution,  care  being  taken  to  arrange  it  as 
nearly  as  possible  equidistant  from  the  sides  and  the  bottom  of 
the  dish,  in  order  to  obtain  as  uniform  a  distribution  of  the  cur- 
rent as  possible.  It  was  considered  best  to  use  a  high  current 
density,  as  most  suitable  for  the  deposition  of  the  peroxide.  The 
current  was  therefore  regulated  to  give  a  strength  of  1.4  amperes, 
which  was  maintained  during  electrolysis.  The  pressure  between 
the  electrodes  was  12  volts  at  the  beginning,  decreasing  to  8.6 
volts  at  the  end.  Almost  immediately  after  the  circuit  had  been 
closed,  a  deep  black,  shining  deposit  appeared  at  the  anode.  The 
current  was  allowed  to  act  for  one  and  one-half  hours,  when  the 
level  of  the  liquid  was  raised  to  ascertain  whether  any  more 
peroxide  would  precipitate.  As  no  further  precipitation  took  place, 
the  liquid  was  siphoned  off  and  replaced  by  water,  without  in- 
terrupting the  current.  The  deposit  showed  a  deep  black,  shining 
color  and  was  firmly  adherent  to  the  dish,  showing  no  tendency 
to  come  off  during  washing.    It  was  washed  carefully  with  water 


and  dried.  Smith1  states  that  it  is  useless  to  try  to  obtain  a 
definite  compound  by  drying  the  deposit,  as  it  is  so  extremely 
hygroscopic,  that  ignition  alone  to  the  protosesquioxide  will  give 
definite  and  concordant  results.  This  was  found  to  be  true. 
Though  the  precipitate  looked  very  well  and  had  quite  a  metallic 
appearance,  it  was  not  possible  to  get  a  concordant  weight,  as  it 
attracted  moisture  very  rapidly.  Following  the  directions  given 
by  Smith  (I.e.)  the  deposit  was  ignited  over  the  Bunsen  burner 
and  the  blast  lamp,  and  thus  changed  to  the  protosesquioxide, 
when  it  could  be  weighed  without  any  trouble.  The  solution, 
when  tested,  failed  to  show  the  presence  of  manganese.  The 
following  table  shows  the  results  of  four  determinations  made  in 
exactly  the  same  manner : 

N.D.iqr  Mn  found. 

Electrolyte.  Time.  Temperature.        at  anode.  Voltage.  Grams. 

10  cc.  MnS04  Ordinary  temp. 

+  5CC.HCOOH  at  start,  heated                     12.0  volts  at     °'"°° 

1.06  sp.  gr.  i1/,  hrs.    up  by  action  of        1.4         start  to  8.6      0"1I05 

-f- 10  cc.=  1  gm.  current  to  400-                    volts  at  end.     0*II07 

sodium  formate.  500  at  the  end. 

It  was  thus  established  that  Kaeppel's  statement,  that  more 
than  five  drops  of  formic  acid  entirely  prevented  the  formation 
of  peroxide  of  manganese,  did  not  hold  true  under  the  conditions 
under  which  the  experiments  were  run.  It  was  further  proved 
that  it  was  very  well  possible  to  deposit  the  whole  of  the  man- 
ganese in  the  presence  of  formic  acid,  even  if  the  acid  was  present 
in  amounts  considerably  above  that  given  by  Kaeppel  as  the 
maximum.  According  to  Classen,2  it  is  necessary  in  the  carrying 
out  of  Engels's  method,  to  weigh  the  platinum  dish  after  the 
deposit  of  peroxide  has  been  removed  from  it,  as  the  dish  suffers 
a  diminution  of  weight  during  electrolysis,  amounting  to  about 
1  mg.  With  the  electrolyte  used  in  the  experiments  under  con- 
sideration this  does  not  take  place,  the  dish  losing  either  no 
weight  at  all  or  at  the  most  only  1/10  mg. 

Though  it  was  evident  from  the  results  tabulated  above  that 
concordant  results  could  be  obtained  in  this  way  by  exactly  dupli- 
cating the  experiments,  yet  the  results  obtained  were  too  high.  It 
was  also  observed  that  even  a  prolonged  ignition  over theblast  lamp 
failed  to  remove  the  hygroscopic  character  of  the  deposit  entirely. 
Though  the  deposit  could  be  weighed  without  any  difficulty,  it 

1  Electrochemical  Analysis,  3rded.,  p.  96. 

2  Ausgewahlte  Methoden,  p.  369. 


8 

continued  to  slowly  attract  moisture,  and  when  standing  over 
night,  had  gained  perceptibly  in  weight. 

Experiments  were  then  conducted  with  a  low  voltage,  so  as  to 
study  the  effect  of  a  lower  current  and  consequently  lower  current 
density  on  the  deposit.  The  character  of  the  deposit,  however, 
remained  unchanged,  the  lower  currents,  of  course,  requiring  a 
proportionately  longer  time  to  effect  the  complete  deposition  of 
the  manganese.  Heating  up  of  the  electrolyte,  to  about  500  or 
550,  had  no  accelerating  effect,  but  it  was  in  so  far  harmful,  as 
it  tended  to  make  the  deposit  blistery  and  was  inclined  to  scale  off. 
It  was  then  tried  to  see  whether  larger  quantities  of  sodium 
formate  would  have  a  beneficial  effect.  It  was,  however,  ascer- 
tained that  larger  quantities  of  that  salt  had  a  decidedly  retardent 
effect.  If  it  was  present  in  quantities  of  2*/2  grams  the  deposition 
was  not  complete  in  less  than  two  and  one-half  hours.  An  in- 
teresting fact  was  revealed  by  the  results,  which  are  tabulated 
below . 


Manganese 
sulphate. 

Formic 

acid. 
1.06  sp.g. 

Sodium 

formate. 

Grams. 

Time. 

Temp. 

N.D100. 

Voltage. 

Mn  found. 

IO 

5 

i     over  night 

ordinary 

O.I8 

3.0 

O.II31 

IO 

5 

1 

4 

" 

0.2I 

4.0 

O.II2I 

IO 

5 

1 

3 

«< 

0.45 

5-o 

0.1 108 

IO 

5 

2 

2 

<< 

I.O 

4-5 

0.1 154 

IO 

5 

2# 

*X 

«( 

1.0 

3-9 

0.1 180 

IO 

5 

*y* 

*% 

(C 

1.0 

3-9 

O.II72 

It  will  be  noted  that  the  amount  of  manganese  found  did  not 
agree  at  all  with  the  amount  found  in  the  experiments 
tabulated  before.  The  amount  of  sodium  formate  present,  as 
well  as  the  time  necessary  for  the  electrolysis  were  both  shown 
to  have  an  influence  on  the  result,  the  weight  of  the  deposit  in- 
creasing with  the  longer  time  and  the  larger  amount  of  sodium 
formate.  The  hygroscopic  nature  of  the  deposits  obtained  was 
very  evident,  it  being  hardly  possible  to  weigh  those  gotten  when 
2,y2  grams  of  sodium  formate  were  present,  even  after  they  had 
been  ignited  over  the  blast  lamp.  The  most  reasonable  explana- 
tion of  this  fact  seemed  to  be  that  the  sodium  formate  was  also 
partly  decomposed  under  the  influence  of  the  current,  with  the 
formation  of  caustic  soda  at  the  kathode.  Some  of  this  caustic 
soda,  being  specifically  heavier  ttfan  the  electrolyte,  falling  down 
to  the  bottom  of  the  dish  anode,  might  easily  have  been  enclosed 


9 

and  held  mechanically  by  the  depositing  peroxide  of  manganese. 
When  the  precipitation  was  slower,  the  same  amount  of  sodium 
formate  being  present,  the  deposit  had  more  time  to  seize  upon 
and  enclose  alkali,  hence  the  greater  weight  of  the  precipitate,  the 
longer  electrolysis  was  continued.  On  the  other  hand,  when 
much  formate  was  present,  a  greater  amount  of  it  would  be  de- 
composed and  considerably  more  alkali  could  get  into  the  deposit. 

It  should  be  noted  in  this  connection  that  careless  washing  of 
the  precipitated  peroxide  was  entirely  excluded,  as  everyone  of 
the  deposits  was  treated  exactly  alike.  Whether  the  above  ex- 
planation is  the  correct  one  has  not  been  ascertained,  as  it  was 
shown  very  soon  by  the  following  experiments  that  good  results 
could  be  obtained  without  the  use  of  sodium  formate.  That  it  is 
a  perfectly  rational  one,  in  view  of  the  results  shown  above  and  of 
the  hygroscopic  character  of  the  deposit,  even  after  ignition,  can 
hardly  be  doubted.  The  tendency  of  the  caustic  alkali  solution, 
which  is  produced  during  electrolysis,  to  fall  down  to  the  bottom 
of  the  vessel,  is  quite  well  known,  as  is  also  the  fact  that  even  in 
ordinary  quantitative  analysis  it  is  a  most  difficult  thing  to  get  a 
precipitate  free  from  alkali. 

It  was  thus  established  that,  though  perfectly  concordant  results 
could  be  obtained  by  using  formic  acid  with  the  addition  of  sodium 
formate,  by  adhering  exactly  to  the  same  conditions,  yet  the 
results  contained  a  source  of  error,  which  would  make  them  prac- 
tically worthless.  However,  the  good  results  obtained  so  far 
with  formic  acid  had  raised  quite  a  doubt  as  to  the  accuracy  of 
Kaeppel's  statement  with  regard  to  formic  acid  preventing  the 
deposition  of  peroxide  of  manganese. 

The  next  step  was,  consequently,  to  do  away  with  the  source  of 
error  traceable  to  the  addition  of  sodium  formate  and  to  try  formic 
acid  alone.  Accordingly,  10  cc.  of  the  manganese  sulphate  solu- 
tion were  taken,  5  cc.  of  formic  acid  of  1.06  specific  gravity  added, 
and  the  solution  subjected  to  electrolysis  in  the  usual  manner. 
The  voltage  required  was  pretty  high,  on  account  of  the  low 
conductivity  of  the  formic  acid,  it  being  17.5  volts  between  the 
electrodes  at  the  start,  with  a  current  strength  of  1  ampere.  As 
the  solution  got  very  warm  in  about  an  hour,  by  the  passage  of 
the  current,  the  voltage  was  decreased  to  7.9  volts,  giving  an 
amperage  of  0.8.  The  deposit  did  not  come  down  as  quickly  as 
when  sodium  formate  was  present,  but  the  manganese  was  all 


IO 


out  after  four  hours.  The  heating  of  the  electrolyte,  as  had  been 
ascertained  before,  did  not  have  a  favorable  influence,  tending  to 
make  the  deposit  blistery.  The  deposited  peroxide  of  manganese 
was  washed  carefully  and  ignited  in  the  usual  way.  The  weight 
of  the  deposit,  calculated  as  Mn,  was  0.1063  gram,  a  value  which 
closely  agreed  with  that  calculated  to  be  present.  It  was  further 
found  that  the  precipitate  was  absolutely  non-hygroscopic  after 
ignition,  and  could  be  weighed  with  perfect  ease.  It  was  left 
purposely  exposed  to  the  action  of  the  atmosphere  over  night  and 
reweighed  on  the  following  morning,  when  the  weight  was  found 
to  be  the  same.  The  appearance  of  the  deposit  was  the  same  as 
that  obtained  before.  Kaeppel1  contends  that  it  is  possible  to 
weigh  the  deposit  after  drying  for  about  two  hours  at  1500  to 
1800,  thus  doing  away  with  the  necessity  of  changing  it  to  the 
protosesquioxide  by  ignition.  This  was  tried,  but  Kaeppel's 
observation  could  not  be  confirmed,  as  the  deposit  attracted 
moisture  too  quickly  to  make  it  possible  to  obtain  reliable  results. 

Another  solution  of  manganese  sulphate  was  then  made  up,  and 
the  manganese  determined  gravimetrically  as  pyrophosphate. 
There  was  0.1034  gram  of  Mn  found  present  in  10  cc.  As  the 
determinations  with  employment  of  the  spiral  of  platinum  wire 
as  kathode  had  necessitated  such  a  high  potential  between  the 
electrodes  in  order  to  obtain  the  necessary  strength  of  current 
and  had  thereby  caused  objectionable  heating-up  of  the  electrolyte, 
it  was  decided  to  adopt  some  means  to  get  along  with  as  low  a 
voltage  as  possible,  which  would   give  the  necessary   current. 

This  could,  of  course,  only  be  accomplished  by  reducing  the 
resistance  of  the  electrolyte,  either  by  increasing  its  conductivity 
by  the  addition  of  a  better  conducting  material,  or  by  increasing 
the  electrode  surface.  As  the  former  course  was  intended  to  be 
avoided,  the  latter  presented  itself  as  the  only  solution.  Accord- 
ingly, a  so-called  basket  electrode  was  used,  being  a  platinum 
dish,  which  conformed  in  shape  to  the  interior  surface  of  the 
roughened  dish  on  which  the  precipitation  of  peroxide  of  man- 
ganese took  place.  It  had  a  surface  of  60  sq.  cm.  and  was  per- 
forated with  holes  to  allow  of  a  better  egress  of  the  gases  set  free 
during  electrolysis  and  a  better  mixing  of  the  solution.  The 
following  table  gives  the  results  of  some  experiments  carried  out 
with  varying  quantities  of  formic  acid  and  varying  quantities  of 
manganese. 

1  I,oc.  cit.,  p.  274. 


II 


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12 

As  will  be  seen  from  the  above  table,  the  results  obtained  by 
electrolysis  agree  very  closely  with  the  gravimetric.  For  some 
reason,  which  has  not  been  further  investigated,  the  addition  of 
sodium  formate  appears  to  have  a  tendency  to  accelerate  the 
deposition,  as  the  metal  was  out  of  the  solution  in  one  and  one-half 
hours  when  sodium  formate  was  present,  while  it  took  two  and 
one-half  hours  for  the  formic  acid  alone.  The  deposits  obtained 
were  all  very  fine  and  beautifully  adherent,  only  with  0.2880  gram 
of  Mn304  a  slight  disposition  towards  loosening  was  noticeable. 
It  was  very  slight  however,  and,  owing  to  the  scaly  nature  of  the 
material  it  was  quite  easy  to  filter  it  out  quickly  on  a  small  filter, 
wash,  dry  and  remove  it  from  the  filter  and  add  it  to  the  bulk  of 
the  material  in  the  dish,  together  with  the  ashes  of  the  filter 
paper. 

It  is  also  apparent  from  the  above  table  that  the  addition  of 
more  than  5  cc.  of  formic  acid  of  1.06  specific  gravity  has  no 
beneficial  effect.  On  the  contrary,  larger  amounts  of  formic  acid 
tend  to  retard  the  precipitation.  Much  less  than  5  cc.  of  formic 
acid  cannot  be  used,  as  there  is  a  tendency  to  form  flakes  of  a 
brown  precipitate  around  the  kathode,  which  has  to  be  brought 
into  solution  again  by  the  addition  of  more  formic  acid. 

Other  experiments  were  run  with  a  view  of  establishing  whether 
the  addition  of  ammonium  formate  would  have  any  accelerating 
or  otherwise  beneficial  effect  on  the  deposit.  Such  was  not  found 
to  be  the  case.  When  ammonium  formate  was  present  in  small 
amounts,  no  better  quality  of  the  deposit  could  be  obtained  than 
could  be  gotten  when  it  was  not  present.  There  was  then  also 
no  decided  effect  upon  the  time  of  precipitation,  the  time  in  all 
cases  being  about  the  same  as  in  the  experiments  run  without 
sodium  formate,  or  being  slightly  in  favor  of  the  latter.  If, 
however,  more  ammonium  formate  was  added,  the  quantity  of 
manganese  sulphate  and  formic  acid  remaining  the  same,  it  was 
quite  apparent  that  a  great  retardation  in  the  time  of  deposition 
took  place  and  a  very  decided  change  for  the  worse  in  the  char- 
acter of  the  deposit.  It  will  be  noticed  in  the  following  table,  for 
instance,  that  the  complete  deposition  of  the  manganese  was 
obtained  in  one  case  where  0.1034  of  Mn  were  present  as  sulphate, 
and  5  cc.  of  formic  acid,  in  two  and  one-half  hours.  The  deposit 
obtained  in  this  case  was  very  satisfactory.  The  addition  of  2  cc. 
of  ammonium  formate  to  this  electrolyte  retarded  the  time  of 


UNIVERSITY 

OF 

complete  deposition  to  four  and  one-half  hours,  and  the  deposit 
obtained  came  off  the  dish  to  a  considerable  extent.  The  same 
same  thing  happened  when  4  cc.  of  ammonium  formate  were 
added  to  an  electrolyte,  which  had  given  satisfactory  results  with 
2  cc.  of  the  salt.  The  ammonium  formate  was  produced  by  neu- 
tralizing the  1.06  specific  gravity  acid  with  ammonia. 


Mn 
present. 

Mn 
found. 

Formic 

acid  1.06 

sp.  gr. 

cc. 

Ammon- 
ium for- 
mate, 
cc. 

Time 
hours.     Temp. 

N.D.joo. 

Volt- 
age. 

Character 
of  deposit. 

0.1034 

O.  IO34 

5 

21/,     ordinary 

0.8  to  1.0 

7-6 

good 

O.IO34 

O.IO36 

5 

2 

4Vi 

0.8 

5.0 

bad 

O.I5SI 

O.I552 

5 

2 

37* 

0.8 

5-2 

good 

O.I55I 

O.I55I 

5 

2 

12            " 

0.25 

3-0 

good 

O.I55I 

O.I547 

5 

4 

7 

0.8 

4-2 

very  bad 

O.I55I 

O.I552 

8 

2 

4 

0.8 

5-o 

good 

O.I55I 

O.I550 

10 

2 

5 

0.8 

4-8 

good 

It  was  further  tried  whether  the  addition  of  chrome  alum,  as 
recommended  by  Engels,  would  have  a  beneficial  effect  when 
added  to  a  formic  acid  electrolyte.  The  electrolyte  in  this  case 
contained  10  cc.  of  manganese  sulphate,  containing  0.1034  gram 
of  manganese,  5  cc.  formic  acid,  and  1  gram  of  chrome  alum. 
The  current  strength  was  1.0  ampere  with  a  pressure  between 
the  electrodes  of  7.0  volts  in  the  beginning  to  5.5  volts  at  the  end. 
The  results  obtained  were,  however,  very  unsatisfactory.  The 
manganese  was  not  all  out  in  seven  and  three-fourths  hours, 
instead  of  two  and  one-half  hours  without  chrome  alum.  The 
current  was  then  reduced  to  0.08  ampere  and  the  experiment  run 
over  night.  The  weight  of  the  deposit  of  protosesquioxide  of 
manganese  gave  0.1500  of  manganese  instead  of  0.1551  gram. 
Metallic  specks  were  visible  on  the  kathode  and  also  in  the 
deposit  immediately  below  the  kathode,  where  they  had  evidently 
fallen  down  from  the  kathode.  A  test  of  the  deposit  on  the 
kathode  showed  the  presence  of  chromium.  Chrome  alum  as  an 
addition  to  this  electrolyte  was  therefore  shown  to  be  out  of  the 
question. 

Recapitulating  the  results  so  far  obtained,  the  following  con- 
clusions may  be  arrived  at : 

1.  The  statement  of  Kaeppel,  that  it  is  not  possible  to  precipitate 
manganese  completely  in  the  presence  of  formic  acid  and  that 
more  than  5  drops  of  this  acid  prevent  the  deposition  of  the 
peroxide  of  manganese  entirely,  is  not  born  out  by  the  experi- 


14 

mental  facts,  obtained  under  the  conditions  described  above.  It 
is  evident,  therefore,  that  the  conditions  under  which  he  per- 
formed his  experiments  must  have  been  different,  and  it  is  a 
cause  for  regret  that  he  did  not  publish  them,  as  some  inter- 
esting comparisons  might  then  be  made. 

2.  It  is  possible  to  obtain  the  deposit  of  peroxide  from  a 
formic  acid  solution  in  a  beautifully  adherent  and  satisfactory 
form,  which  can  be  washed  and  ignited  without  any  trouble. 
Even  the  ignition  has  no  tendency  to  loosen  the  deposit.  The 
deposits  up  to  0.2851  of  Mn304  do  not  show  any  tendency  to  scale 
off.  This  tendency,  however,  manifests  itself  when  the  man- 
ganese content  of  the  solution  is  higher,  but  even  then  it  is  very 
small. 

3.  Formic  acid  is  a  better  electrolyte  than  acetic  acid,  it  being 
only  possible,  according  to  Classen's  statement  cited  above,  to 
deposit  0.08  gram  of  manganese  in  the  form  of  peroxide. 

As  it  was  thus  ascertained  that  the  deposition  of  manganese 
could  be  performed  easily  and  satisfactorily  in  an  electrolyte  which 
contained  formic  acid,  the  question  arose  as  to  whether  it  would 
also  be  possible  to  effect  the  separation  of  manganese  from  other 
metals  and  especially  from  iron.  The  latter  had  not  been  satis- 
factorily accomplished  at  all  up  to  the  present  time,  as  will  appear 
from  the  following  quotations :  Neumann1  says  in  regard  to  the 
separation  of  iron  and  manganese:  "A  great  number  of  experi- 
ments have  been  carried  out  with  all  forms  of  salts  in  order  to 
discover  a  reliable  method  for  obtaining  a  complete  separation  of 
these  two  metals,  but  without  success.  In  most  of  these  experi- 
ments the  aim  has  been  to  obtain  the  manganese  as  peroxide  at 
the  anode  or  to  keep  it  in  solution,  while  the  iron  is  deposited  at 
the  kathode.  The  results  obtained  showed  that  the  deposition  of 
the  iron  was  incomplete  (at  least  for  the  first  deposition),  and 
that  when  the  manganese  was  separated  as  peroxide,  this  latter 
contained  iron. 

This  difficulty  arises  in  connection  with  the  method  proposed  by 
Classen.2  The  solution  of  the  two  metals  is  prepared  by  treating 
it  with  6  or  8  grams  of  ammonium  oxalate,  and  after  heating  to 
500  or  6o°  C.  the  electrolysis  is  conducted  with  a  current  of  1 

1  "  The  Theory  and  Practice  of  Electrolytic  Methods  of  Analysis,"  translated  by  Ker 
shaw,  London,  1898. 

2  Electrolysis. 


15 

ampere  in  density  and  of  3.1  to  3.8  volts  as  regards  electromotive 
force.  Only  a  small  portion  of  the  manganese  is  obtained  at  the 
anode  as  peroxide  under  these  conditions.  If  less  ammonium 
oxalate  be  used,  permanganic  acid  and  its  salts  will  be  formed  at 
first  at  the  anode  and  later  a  peroxide  deposit  will  be  obtained 
containing  iron.  As  a  rule,  the  liquid  is  rendered  completely 
turbid  by  a  brown  flocculent  precipitate,  which  partly  settles  in 
adherent  form  upon  the  kathode.  The  method  gives  inexact  results 
in  spite  of  all  assertions  to  the  contrary. 

The  method  proposed  by  Brand,1  in  which  a  solution  containing 
sodium  pyrophosphate  and  ammonium  oxalate  and  ammonium 
oxalate  is  used,  also  yields  inaccurate  results. 

If  one  attempt  to  effect  the  separation  of  iron  from  manganese 
in  a  solution  containing  20  to  30  grams  of  ammonium  acetate 
an  incomplete  deposition  of  the  manganese  as  peroxide  occurs, 
owing  to  the  formation  of  a  ferrous  salt,  which  dissolves  the  per- 
oxide again  at  the  anode.  Engels2  has  proposed  to  use  oxidizing 
agents  in  order  to  overcome  this  difficulty.  If  chromic  acid  be 
used  to  oxidize  the  ferrous  salt  a  complete  deposition  of  the 
manganese  as  peroxide  can  be  obtained,  but  the  deposit  will  be 
found  to  contain  up  to  0.02  gram  iron,  probably  in  the  form  of 
oxide." 

Classen3  says:  "The  hope  that  manganese  in  the  presence  of 
iron  might  be  separated  and  determined  in  an  acetic  acid  solution 
has  not  been  fulfilled.  Innumerable  experiments,  conducted  under 
the  most  varied  conditions  and  with  the  most  diverse  substances, 
have  given  no  satisfactory  results.  In  view  of  the  great  im- 
portance which  a  method  for  the  direct  determination  of  man- 
ganese in  the  presence  of  iron,  etc.,  would  possess,  this  investi- 
gation will  be  continued."  Nothing  further  has  been  published 
by  Classen  up  to  now  on  this  subject,  consequently  it  must  not 
have  been  possible  to  make  the  method  work. 

Kaeppel,  in  his  paper  repeatedly  referred  to,  publishes  also  a 
method  for  the  separation  of  iron  and  manganese.  His  acetone 
method  had  failed  completely  to  give  satisfactory  results.  He 
prepares  his  electrolyte  by  bringing  a  solution  of  12  grams  of 
sodium  pyrophosphate  to  boiling,  and  adding,  while  stirring,  a 
solution  of  ferrous  ammonium  sulphate  and  manganese  ammo- 

1  Ztschr.  anal.  Chem.,  a8,  581. 
J  Ztschr.  Electrochemie,  a,  414. 
»  Electrolysis,  p.  149. 


i6 

nium  sulphate.  After  the  solution  has  become  clear  he  adds  5 
drops  of  phosphoric  acid.  If  a  turbidity  is  caused  by  the  addition 
of  the  phosphoric  acid  the  solution  is  clarified  again  by  the  addi- 
tion of  a  few  drops  of  sodium  pyrophosphate  solution.  The  metal- 
lic salt  solutions  contained  0.1  to  0.15  gram  of  iron  and  0.035  to 
0.11  gram  of  manganese.  The  deposition  of  the  iron  takes  eight 
and  one-half  to  nine  and  one-half  hours,  and  it  is  not  possible 
to  determine  the  manganese  electrolytically  in  the  solution  after 
the  iron  is  out.  Electrolysis  takes  place  at  a  temperature  of  300 
to  400  C. 

It  was  therefore  an  interesting  question  whether  it  was  possible 
to  find  a  solution  in  which  the  iron  and  manganese  could  be 
separated.  As  the  manganese  peroxide  deposits  on  the  anode 
and  the  iron  on  the  kathode  it  should  be  theoretically  possible  to 
obtain  both  of  them  at  the  same  time.  The  beautiful  character 
of  the  deposits  obtained  by  the  use  of  formic  acid  gave  rise  to  the 
hope  that  it  might  be  easily  possible  to  separate  the  two  metals  in 
such  a  solution.  Before  going  to  this  separation,  however,  the 
method  was  first  tried  on  the  separation  of  zinc  and  manganese. 
A  solution  of  zinc  sulphate,  containing  a  calculated  amount  of 
0.1  gram  of  metal  in  10  cc,  was  used.  Electrolysis  was  carried 
out  in  the  usual  manner,  a  roughened  platinum  dish  serving  as 
anode,  while  the  platinum  basket  electrode  was  connected  as 
kathode.  It  was  found  that  the  deposit  of  zinc  showed  an  extreme 
tendency  to  come  down  in  spots  upon  the  kathode,  and  the  basket 
electrode  had  to  be  carefully  adjusted  so  that  it  was  equidistant 
from  the  sides  of  the  dish.  It  was  also  found  that  in  this  case 
the  addition  of  ammonium  formate  seemed  to  exert  beneficial  in- 
fluence on  the  character  of  the  zinc  deposit,  the  best  results  being 
obtained  with  a  solution  containing  10  cc.  of  a  manganese  sulphate 
solution  with  0.1034  gram  of  manganese,  10  cc.  zinc  sulphate 
solution  with  0.1000  gram  of  zinc,  10  cc.  of  formic  acid  of  1.06 
specific  gravity  and  5  cc.  of  a  solution  of  ammonium  formate 
obtained  by  neutralizing  1.06  specific  gravity  formic  acid  by 
ammonia.  The  following  table  shows  some  of  the  results  obtained  : 


Mn 

Mn 

Zn 

Zn          Time.    Tempera-   N.D.ioo 

N.D.jqo 
kathode. 

Volt- 

present. 

found. 

present. 

found.      Hours.         ture.       anode. 

age. 

O.IO34 

O.IO37 

O.IOOO 

0.0998         11       ordinary     1.0 

1.66 

5-4 

O.IO34 

O.I033 

O.IOOO 

O.OIOOI        11^           "              1.0 

1.66 

5.4 

O.I034 

O.I036 

O.IOOO 

0.01003       IJ             "            I-° 

1.66 

5-4 

*7 

After  this  question  had  been  satisfactorily  solved,  the  chances 
seemed  to  be  very  promising  that  iron  might  be  easily  separated 
from  manganese  in  a  formic  acid  solution.  But  these  hopes 
seemed  to  be  doomed  to  disappointment,  for  when  a  separation 
was  tried  under  the  conditions  which  had  proved  most  successful 
for  manganese  alone,  not  much  of  a  result  was  obtained,  even  if 
electrolysis  was  continued  for  twelve  hours.  The  electrolyte  in 
that  case  consisted  of  10  cc.  of  a  ferric  ammonium  sulphate  solu- 
tion, containing  o.iooo  gram  of  metallic  iron,  10  cc.  manganese 
sulphate,  containing  0.1034  gram  manganese  and  5  cc.  formic 
acid.  The  basket  electrode  served  as  kathode  and  the  dish  as 
anode.  A  long  series  of  experiments  were  then  started  in  order 
to  ascertain  the  best  conditions  for  a  separation.  It  was  first 
tried  to  obtain  a  better  result  by  varying  the  amount  of  formic 
acid  in  the  solution.  It  was  found  that  10  cc.  of  the  acid,  with  the 
same  amount  of  iron  and  manganese  present  as  above,  gave  the 
best  results,  but  they  were  still  far  from  quantitative.  In  order 
to  ascertain  whether  the  substitution  of  a  ferrous  sulphate  solution 
for  the  ferric  ammonium  sulphate  solution  would  prove  beneficial, 
electrolytes  were  tried,  containing  FeS04,  but  the  results  obtained 
were  still  less  encouraging  than  those  gotten  before.  It  was 
thought  that  various  current  densities  at  the  anode,  as  well  as  at 
the  kathode,  might  have  an  influence  on  the  result  and  perhaps 
bring  more  success.  Accordingly,  the  current  density  was  varied 
at  the  anode  from  N.D.100  =  0.15  to  N.  D.100  =  2.8.  The  current 
density  at  the  kathode  was  also  varied  from  N.D.100  =  o.i5to47  by 
using  spiral,  basket  and  gauze  electrodes,  but  the  result  was  unsatisr 
factory.  It  was  also  tried  to  see  whether  a  uniform  current 
density  at  the  electrodes  would  prove  beneficial,  and  therefore  a 
number  of  experiments  were  made  by  introducing  the  solution 
into  a  beaker  glass  and  suspending  into  it  two  platinum  gauze 
electrodes,  arranged  exactly  opposite  each  other.  This  was  again 
unsuccessful,  for  not  only  was  it  impossible  to  get  the  two  metals 
out  completely,  but  at  the  edge  of  the  kathode  there  formed  a 
small  deposit,  consisting  of  a  brown  colored  manganese  compound, 
as  was  ascertained  by  scraping  some  of  it  off  and  testing  it.  It 
was  noticed  in  all  of  this  work  that,  in  order  to  obtain  the  iron 
free  from  manganese,  it  was  absolutely  essential  to  have  the  cur- 
rent density  at  the  kathode  entirely  uniform,  that  is  to  say,  all 
parts  of  the  kathode  had  to  be  equidistant  from  the  anode  surface. 


i8 

If  there  was  one  point  of  the  kathode  nearer  to  the  anode  there 
was  danger  of  some  oxide  of  manganese  depositing  there.  Per- 
haps this  fact  is  an  explanation  why  it  has  not  been  possible  to 
obtain  concordant  results  with  methods  proposed  up  to  the  present 
time,  when  they  were  worked  by  different  investigators. 

Electrodes  of  sheet  platinum  were  also  tried.  The  results  from 
all  these  trials  were  disappointing,  for,  though  the  separation  of 
the  two  metals  could  be  effected,  one  metal  not  containing  any  of 
the  other,  yet  it  was  impossible  to  get  all  of  the  metals  out  of  the 
solution  even  in  periods  varying  from  eleven  to  twelve  hours. 

As  the  addition  of  ammonium  formate  had  proved  beneficial  in 
the  case  of  zinc,  experiments  were  also  carried  out  with  the  addition 
of  varying  amounts,  from  I  to  15  cc,  obtained  by  neutralizing 
formic  acid  of  1.06  specific  gravity  with  ammonia,  to  varying 
amounts  of  formic  acid,  from  5  to  20  cc.  1.06  specific  gravity. 
Its  presence  in  small  quantity  was  found  to  have  a  beneficial 
effect,  as  a  greater  amount  of  iron  was  obtained,  but  it  was  not 
possible  to  get  all  the  iron  out  even  when  the  electrolysis  was 
continued  for  more  than  twelve  hours.  Additions  of  formal- 
dehyde, in  small  quantity,  were  found  to  retard  the  precipitation 
of  manganese,  though  they  had  no  effect  upon  accelerating  the 
deposition  of  iron. 

It  was  then  decided  to  see  whether  it  was  not  possible  to  separate 
the  two  metals  by  retarding  or  preventing  the  deposition  of 
peroxide  of  manganese  altogether.  Accordingly,  the  use  of  formic 
acid  was  abandoned  for  the  time  being,  and  as  experiments  had 
proved  that  in  an  electrolyte  of  tartaric  acid  the  manganese  was 
almost  completely  held  up,  it  was  decided  to  try  this  acid  in 
conjunction  with  formaldehyde,  which  had  also  been  found  to 
have  a  retardent  effect  on  the  manganese.  As  ammonium  formate 
had  been  found  to  have  a  beneficial  effect  on  the  deposition  of 
the  iron,  it  was  used  in  conjunction  with  the  other  two.  In  order 
to  obtain  as  high  a  conductivity  of  the  solution  as  possible  and  to 
get  along  with  as  small  a  voltage  as  possible  and  yet  obtain  the 
high  current  strength  necessary  for  precipitating  the  iron,  an 
addition  of  3  grams  of  ammonium  sulphate  was  made  to  the 
electrolyte.  This  finally  led  to  the  desired  result.  In  an  electrolyte 
of  this  kind  a  complete  and  thorough  separation  of  the  iron  and 
manganese  could  be  effected.  Electrolysis  was  conducted  in  the 
following  manner:     The  electrolyte  contained   10  cc.  of  man- 


19 

ganese  sulphate  solution,  containing  0.1034  gram  of  manganese, 
and  10  cc.  of  a  ferric  ammonium  sulphate  solution  containing 
0.1003  gram  of  iron.  To  this  were  added  10  cc.  of  a  ammonium 
formate  solution,  made  as  described  above,  by  neutralizing  1.06 
specific  gravity  acid  by  ammonia,  and  10  cc.  of  an  ammonium 
sulphate  solution  containing  3  grams  of  this  salt.  1  cc.  of  a  solu- 
tion of  45  per  cent,  formaldehyde  was  also  added.  The  platinum 
dish  was  used  as  kathode,  and  the  basket  electrode,  which  had 
been  used  before,  was  introduced  as  anode.  The  basket  electrode 
was  chosen  in  order  to  provide  as  much  anode  surface  as  possible 
for  the  deposition  of  any  manganese  peroxide  which  might  be  de- 
posited there,  and  thus  assure  its  adhering  to  the  anode.  The 
solution  was  then  made  up  to  130  cc,  in  order  to  cover  as  nearly 
as  possible  100  sq.  cm.  of  the  dish.  Electrolysis  was  conducted 
in  the  cold,  with  a  voltage  between  electrodes  of  3.5  volts  and 
an  amperage  of  1.4  amperes,  the  N.D.100  at  the  anode  being  con- 
sequently 2.33  and  at  the  kathode  1.4.  The  iron  deposited  in 
from  three  to  five  hours  in  a  beautiful  form,  and  not  a  trace  of  it 
could  be  detected  in  the  solution.  The  deposit,  when  tested,  also 
proved  to  be  entirely  free  from  manganese.  A  little  bit  of  peroxide 
of  manganese  precipitated  on  the  anode  in  a  beautifully  adherent 
form,  but  only  from  0.0055  to  0.006  gram  of  peroxide  had  de- 
posited at  the  end  of  the  electrolysis  when  the  iron  was  all  out. 
No  peroxide  was  swimming  in  the  electrolyte  and  the  solution 
was  colored  red  from  the  permanganic  acid  formed.  It  was  soon 
found,  however,  that  the  deposit  of  iron  could  not  be  weighed, 
as  it  contained  varying  and  sometimes  considerable  amounts  of 
carbon.  The  odor  of  hydrocarbons  was  quite  perceptible  on  dis- 
solving the  deposited  metal  in  dilute  sulphuric  acid,  and  a  residue 
was  left  on  the  dish  after  this  operation,  which  could  be  volatil- 
ised by  igniting  the  dish.  This  carbon  content  proved,  however, 
no  obstacle  to  a  successful  determination  of  the  iron,  as  it  was 
easily  possible  to  dissolve  the  deposit  of  the  dish  very  quickly  by 
introducing  some  distilled  water  and  a  few  cc.  of  concentrated 
sulphuric  acid.  The  solution  was  then  transferred  to  a  beaker 
and  boiled  for  a  few  minutes  in  order  to  get  rid  of  the  hydro- 
carbons. A  little  granulated  zinc  was  then  added  in  order  to  re- 
duce any  iron  which  might  have  become  oxidized,  and  the  solu- 
tion was  then  titrated  with  a  very  dilute  standardized  solution  of 
potassium  permanganate.     The  whole  manipulation  in  this  way 


20 

consumed  perhaps  less  time  than  the  drying  and  weighing  of  the 
dish  would  have  done.  The  following  table  gives  the  results  of  a 
number  of  experiments,  run  in  the  way  above  described. 

The  solution,  when  taken  off,  had  a  fishy  smell,  due  to  decom- 
position products  of  the  formaldehyde.  The  addition  of  the 
latter  was  discontinued  after  it  had  been  shown  by  experiments 
that  its  presence  had  no  influence  on  the  result.  The  fishy  smell 
of  the  solution  did  not  appear  any  more  after  formaldehyde  was  no 
longer  used.  Results  with  and  without  formaldehyde  are  given 
in  the  above  table. 

Though  it  was  shown  by  these  experiments  that  in  an  electro- 
lyte composed  as  above,  a  successful  separation  of  the  iron  and 
manganese  could  be  accomplished  in  much  less  time  than  by  the 
method  of  Kaeppel,  as  cited  above,  and  a  method,  which  would 
also  work  in  the  presence  of  a  large  amount  of  manganese,  yet  it 
was  felt  that  only  half  the  problem  had  been  solved  in  this  way. 
The  fact  that  the  manganese  could  not  be  determined  electro- 
lytically  after  the  iron  was  all  out,  and  anyway,  the  fact  that  it 
had  to  be  held  up  and  thus  prevented  from  deposition,  were  suffi- 
cient stimulants  to  renew  the  effort  of  finding  a  method  by  which 
the  two  metals  could  be  determined  simultaneously.  It  was  felt 
that  the  experiments  with  formic  acid  had  given  considerable  en- 
couragement, and  all  that  was  needed  was  to  find  some  addition 
to  the  electrolyte  for  the  purpose  of  accelerating  the  deposition. 
Accordingly,  the  experiments  with  formic  acid  were  resumed. 

The  electrolyte,  which  had  been  found  most  favorable  formerly, 
contained  10  cc.  of  manganese  sulphate,  10  cc.  of  ferric  ammonium 
sulphate  and  10  cc.  formic  acid  of  1.06  specific  gravity.  The 
desired  result  was  first  thought  might  be  obtained  by  the  use  of 
an  oxidizing  agent.  As  such  nitric  acid  was  chosen,  and  various 
additions,  from  10  drops  to  10  cc.  of  concentrated  acid  were 
made.  It  was  found,  however,  that  this  had  the  effect  of  pre- 
venting the  deposition  of  iron  altogether  and  that  of  manganese 
to  a  large  extent.  It  was  therefore  abandoned  and  the  addition 
of  a  reducing  substance  tried.  Sodium  sulphite  was  chosen  as 
such,  and  34  gram  of  it  added  to  the  solution.  This  had  the  effect 
of  bringing  out  the  deposit  of  peroxide  of  manganese  in  shorter 
time  than  before,  and  a  very  fine  deposit  of  iron,  but  in  six  and 
one-half  hours  neither  all  the  iron  nor  all  the  manganese  was  out 


21 


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22 

of  the  solution.  A  larger  amount  of  sodium  sulphite  was  evi- 
dently needed,  but  when  y^.  gram  of  it  was  introduced  into  the 
solution  the  salt  was  itself  decomposed  under  the  action  of  the 
current,  with  a  liberation  of  sulphur  all  through  the  electrolyte. 
As  it  was  considered  undesirable  to  have  this  precipitate  of  sul- 
phur in  the  solution,  as  it  might  contaminate  the  deposits  and 
interfere  with  the  results,  it  was  then  tried  to  add  the  sodium 
sulphite  at  intervals  during  electrolysis,  a/10  gram  at  a  time.  This 
was  carried  out  and  was  soon  found  to  be  effective  in  removing 
the  iron.  Electrolysis  was  carried  out  as  usual  in  the  roughened 
platinum  dish  with  the  basket  platinum  electrode,  it  having  been 
found  by  repeated  trials  that  a  spiral  kathode  could  not  be  used, 
as  there  was  invariably  a  precipitate  of  oxide  of  manganese  on  it, 
especially  on  he  outer  rim,  which  was  nearest  to  the  anode. 
This  was  evidently  due  to  a  high  current  density  at  the  kathode 
and  was  in  line  with  observations  mentioned  above.  The  elec- 
trolyte was  made  up  in  such  a  manner  that  10  cc.  of  a  solution, 
containing  1/10  gram  of  sodium  sulphite,  were  introduced  into  the 
dish  and  the  ferric  ammonium  sulphate,  10  cc.  containing  0.0997 
gram  of  iron,  was  added.  The  solution  immediately  acquired  a 
very  dark  red  color.  The  usual  10  cc.  of  MnS04  were  then  added, 
and  after  that  the  formic  acid  solution.  5  cc.  of  formic  acid  of 
1.06  specific  gravity  were  found  to  answer  well.  It  was  found 
that  the  addition  of  1  cc.  of  a  sodium  sulphite  solution,  containing 
V10  gram  in  1  cc.  for  every  half  hour  at  the  beginning  for  2 
times,  and  an  addition  of  an  equal  amount  every  hour  until  the 
iron  was  out,  answered  well.  A  very  good  indication  of  the 
gradual  deposition  of  the  iron  is  furnished  by  the  fact  that  on 
each  addition  of  sodium  sulphite  the  color  of  the  solution  deepens 
quite  perceptibly,  the  coloring  getting  weaker,  the  less  iron  is 
present.  When  only  traces  of  iron  are  left  in  the  solution  it  does 
not  color  any  more  on  the  addition  of  sodium  sulphite.  It  has  then 
to  be  watched  and  tested  for  iron  from  time  to  time,  until  no 
reaction  is  obtained  any  more.  Care  must  be  taken  in  this  connec- 
tion that  the  electrode  with  the  iron  deposit  on  it  be  taken  out  as 
soon  as  no  reaction  for  iron  can  be  obtained.  If  that  is  not  done 
there  is  danger  of  some  of  the  iron  going  into  solution  again 
if  left  too  long.  The  basket  electrode  is  then  removed,  washed  off 
and  an  auxiliary  spiral  electrode  inserted  as  quickly  as  possible 


23 

into  the  solution  in  order  to  prevent  the  peroxide  of  manganese, 
which  has  precipitated,  from  dissolving  in  the  electrolyte.  Care 
must  be  taken  during  the  time  that  this  spiral  electrode  is  in  the 
solution,  to  insert  resistance  into  the  circuit,  so  as  to  cut  down 
the  current  to  o.i  ampere  or  less,  in  order  to  prevent  anything 
from  precipitating  on  the  spiral  electrode.  If  this  precaution  be 
not  taken  there  will  invariably  be  a  brown-looking  deposit  on  the 
electrode.  The  basket  electrode  with  the  deposit  of  iron  on  it  is 
introduced  into  a  small  beaker  and  covered  with  distilled  water. 
A  few  cc.  of  concentrated  sulphuric  acid  are  then  added  and  the 
solution  of  the  iron  will  take  place  rapidly.  The  basket  is  then 
washed  off  and  reintroduced  into  the  electrolyte,  after  the  spiral 
electrode  has  been  taken  out.  5  cc.  of  formic  acid  of  1.06  specific 
gravity  is  then  added,  and  the  current  raised  to  its  original  value 
again  for  the  purpose  of  precipitating  the  rest  of  the  manganese. 
A  little  granulated  zinc  is  then  introduced  into  the  iron  solution 
for  the  purpose  of  reducing  any  of  the  metal  which  has  oxidized 
during  the  time  that  the  auxiliary  kathode  was  introduced,  and 
the  iron  is  then  titrated  in  the  usual  manner.  It  is  not  possible 
to  obtain  the  iron  by  weighing,  for,  though  a  fine  looking  deposit 
is  obtained,  there  is  invariably  some  slight  oxidation  during  the 
time  necessary  to  change  electrodes.  The  results  obtained  are 
shown  in  the  following  table  and  are  very  satisfactory  and 
concordant. 


Fe 
present. 

Fe 

found. 

Mn 
present. 

Formic 

acid  1.06. 

cc 

Sodium 
sulphite. 

Time. 

Temp. 

kathode. 

Volt- 
age. 

O.IOIO 

0.1008 

0.0988 

5 

6  additions 
Viogm.  each 

41/, 

ordinary 

1.2 

4.4 

O.IOIO 

0.1008 

0.0988 

5 

<« 

5 

" 

1.2 

4.4 

O.IOIO 

O.IOIO 

0.0988 

5 

11 

5 

<« 

1.2 

44 

O.IOIO 

0.1008 

0.0988 

5 

«« 

5 

<« 

1.2 

4-4 

O.IOIO 

O.IOII 

0.0494 

5 

11 

41/. 

«« 

1.2 

4-4 

O.IOIO 

0.1007 

0.0494 

5 

11 

4Vi 

<( 

1.2 

4.4 

O.IOIO 

O.IOIO 

0.0494 

5 

<< 

5 

(i 

1.2 

4.4 

O.IOIO 

0.1009 

0.0988 

5 

11 

5 

<  t 

1.2 

4.4 

O.IOIO 

O.IOII 

0.0988 

5 

1  c 

5 

11 

1.2 

4-4 

O.IOIO 

0.1007 

0.0988 

5 

(< 

5 

11 

1.2 

4-4 

O.IOIO 

O.IOII 

0.0988 

5 

<< 

5 

<< 

1.2 

4.4 

It  was  thus  establshed  that  the  separation  of  iron  and  man- 
ganese could  also  be  effected  in  an  electrolyte,  consisting  mainly 
of  formic  acid.     It  was  found,  however,  that  though  the  sodium 


24 

sulphite  was  very  effective  as  far  as  the  iron  was  concerned,  it 
acted  as  a  retarding  agent  upon  the  manganese,  inasmuch  as  it 
was  found  impossible  to  remove  the  last  traces  of  manganese  in 
any  reasonable  time.  When  only  0.0494  gram  of  manganese  were 
present,  the  complete  deposition  could  be  effected  in  about  ten  to 
eleven  hours,  but  thirteen  or  fourteen  hours  were  needed  for 
0.0988  gram  of  manganese.  The  precipitate  obtained  at  the  end 
of  electrolysis,  when  all  the  manganese  was  deposited,  was  not 
adherent,  though  at  the  time  when  the  electrode  with  the  iron 
deposit  on  it  was  removed  the  deposit  of  manganese  peroxide 
appeared  adherent.  This  was  probably  due  to  the  action  of  the 
large  amount  of  gas  set  free  at  the  anode,  as  the  electrolysis  had 
to  be  continued  such  a  long  time  in  order  to  bring  out  the  last 
traces  of  the  manganese.  However,  this  fact  of  the  precipitate 
being  loose,  was  not  considered  very  much  of  a  drawback,  as  the 
experiments  mentioned  in  the  beginning  had  shown  that  the 
presence  of  a  sodium  compound  in  the  electrolyte  was  not  desirable 
when  the  precipitate  of  manganese  peroxide  was  adherent.  The 
precipitate,  moreover,  was  scaly  and  very  heavy,  and  settled  rap- 
idly down  to  the  bottom  of  the  beaker,  to  which  the  siphoned-off 
solution  was  transferred.  The  solution  in  these,  as  in  all  other 
experiments  was  replaced  by  distilled  water,  while  the  current 
was  still  running,  and  the  current  then  interrupted.  As  the 
precipitate  settled  down  to  the  bottom,  the  supernatant  liquid 
could  be  almost  entirely  decanted  off  and  the  precipitate  filtered 
quickly  and  washed  thoroughly.  The  washing  was  performed 
with  hot  water  and  continued  for  some  time,  in  order  to  remove 
any  alkali  which  might  be  present.  The  filter  was  then  dried, 
the  precipitate  brushed  into  the  dish,  the  filter  burned  separately 
and  the  ashes  added  to  the  material  in  the  dish,  after  which  the 
dish  was  ignited  in  the  usual  manner.  The  results  obtained  were 
very  satisfactory  as  far  as  separation  is  concerned,  as  is  shown  by 
the  following  table : 


25 


ft 

■o" 

c 

1 

g 

1 

i 

c 

a 

e 

1 

c 

■0 

I 

c 

£ 

s 

1 

do 

8 

s 
is 

e 
1 

s 

1 

a 
8 

(J 
55 

I 

8 

Q 

0 

fee 
a 

> 

6inst 

ments 

ordi- 

O.IOIO 

O.IOII 

0.0494 

0.0499 

5 

V10 

gm 

each. 

10 

nary. 

2.0 

1.2 

4-4 

O.IOIO 

0.1007 

0.0494 

0.0497 

5 

1 

n# 

" 

2.0 

1.2 

4.4 

O.IOIO 

O.IOIO 

0.0494 

0.0497 

5 

« 

ti 

<« 

2.0 

1.2 

4-4 

O.IOIO 

0.1008 

0.0988 

0.0990 

5 

< 

i2# 

" 

2.0 

1.2 

4-4 

O.  IOIO 

0.1008 

0.0988 

0.0994 

5 

1 

U 

" 

2.0 

1.2 

4-4 

O.IOIO 

O.IOIO 

0.0988 

0.0987 

5 

< 

14 

M 

2.0 

1.2 

4.4 

O.IOIO 

O.IOII 

0.0988 

0.0992 

5 

' 

H 

" 

2.0 

1.2 

4-4 

The  problem  of  the  separation  of  the  iron  and  manganese  and 
the  electrolytic  determination  of  manganese  in  the  same  solution 
had  thus  been  solved,  but  unfortunately  the  time  required  was  very 
long  and  probably  too  long  to  make  the  method  of  practical  value. 
The  next  experiments  were  therefore  undertaken  with  a  view  to 
reduce  the  time  necessary  for  the  complete  precipitation  of  the 
manganese,  after  the  iron  was  out.  Various  means  were  adopted 
to  accomplish  this,  the  first  being,  as  would  naturally  suggest  itself 
from  the  usual  practice,  to  raise  the  current  in  order  to  get  the  last 
traces  out.  It  was  soon  found,  however,  that  this  method  did  not 
work  in  this  case,  and  that  there  was  danger,  if  the  current  was 
raised  above  1.4  amperes,  that  some  manganese  compound  would 
precipitate  on  the  kathode.  This  would  take  place  to  a  consider- 
able degree  if  the  current  was  raised  to  2  amperes,  corresponding 
to  a  current  density  at  the  kathode  of  N.D.100  =  3.3,  an  at  the 
anode  of  N.D.100  =  1.6  to  2 

Varying  amounts  of  ammonium  formate  were  then  introduced, 
but  did  not  prove  beneficial.  Additions  of  hydrogen  peroxide  up 
to  10  cc.  of  a  3  per  cent,  solution  also  did  not  improve  matters,  for 
while  they  evidently  had  some  action  on  the  deposit,  in  making  it 
more  adherent,  yet  the  last  traces  of  the  manganese  did  not  come 
out  any  faster,  but  rather  the  reverse.  Additions  of  alcohol  in 
quantities  up  to  10  cc.  and  of  acetone  of  5  and  10  cc.  did  not  have 
a  beneficial  effect.  Considerable  time  was  thus  spent  in  trying  to 
reduce  the  time  for  the  precipitation  of  manganese,  but  no  headway 
could  be  made. 

It  was  then  decided  to  see  whether  ammonium  acetate  would 
prove  of  value  in  this  connection  and  a  solution  was  made  by 


26 

neutralizing  ordinary  acetic  acid  of  1.06  specific  gravity  with 
ammonia,  to  a  barely  acid  reaction.  An  experiment  was  run  in 
the  usual  manner  with  addition  of  sodium  sulphite,  until  the  iron 
was  out  and  removed.  Ten  cc.  of  the  ammonium  acetate  solution 
were  then  added  and  the  electrolysis  continued.  The  result  was 
quite  surprising,  for  after  two  hours  the  level  of  the  solution  was 
raised  and  it  was  observed  that  no  manganese  peroxide  deposited 
any  more.  When  the  solution  was  tested,  no  manganese  was 
found  to  be  present.  The  time  of  deposition  of  the  peroxide  had 
thus  already  been  cut  down  from  thirteen  or  fourteen  hours  to 
seven  hours.  The  deposit  weighed  0.0992  gram  while  0.0988  was 
present. 

As  it  was  felt  that  the  presence  of  sodium  sulphite  in  the  elec- 
trolyte was  not  altogether  desirable  and  that  it  would  be  better,  in 
order  to  remove  all  possible  sources  of  error,  if  the  separation 
could  be  effected  without  introducing  it,  the  next  endeavor  was 
made  in  the  direction  of  reducing  its  quantity.  Incidentally  it  was 
also  desirable  to  cut  down  the  time  required  for  the  deposition  of 
the  iron  and  to  do  away  with  the  necessity  of  removing  the  basket 
electrode,  after  the  iron  had  all  deposited  on  it,  in  order  to  prevent 
any  re-solution.  Accordingly  ammonium  acetate  was  introduced 
from  the  start  and  the  quantity  of  sodium  sulphite  was  cut  down  to 
3  cc.  =  0.3  gram  and  2  ec.  =  0.2  gram.  For  precaution's  sake  the 
basket  electrode,  with  the  major  part  of  the  iron  on  it,  was  also 
removed,  but  it  was  found  that  93  per  cent,  of  the  iron  had  already 
deposited  in  two  hours,  and  the  rest  was  found  when  the  elec- 
trode was  removed  at  the  end  of  the  electrolysis.  The  surprising 
result  was  found  that  the  iron  and  manganese  were  all  out  of  the 
solution  at  the  end  of  four  hours.  The  iron  was  titrated  as  usual 
and  the  manganese  peroxide  filtered  off  and  the  results  agreed  very 
closely  with  the  amounts  present  in  the  solution.  It  was  then 
tried  to  reduce  the  quantity  of  sodium  sulphite  still  further  and  to 
add  only  10  drops,  corresponding  to  only  0.05  gram  of  the  salt. 
It  was  found,  that  the  separation  could  be  effected  just  as  satisfac- 
torily as  before,  and  that  the  electrode  with  the  deposit  of  iron  on 
it,  did  not  have  to  be  removed  from  the  solution.  The  complete 
deposition  of  the  two  metals  was  again  accomplished  in  four  hours. 
The  next  step  was  then  to  try  and  get  along  without  the  sodium 
sulphite  altogether  and  it  was  finally  ascertained  that  if  was  not 


27 

necessary  to  add  any  of  it.  The  separation  took  place  just  as  well 
in  formic  acid  solution,  to  which  only  ammonium  acetate  had  been 
added.  However,  as  had  already  been  noted  in  the  beginning  of 
these  experiments  and  mentioned  there  in  connection  with  the  use 
of  sodium  formate,  the  sodium  salts  seem  to  have  an  accelerating 
effect  upon  the  precipitation  of  the  manganese.  Just  in  the  same 
manner  as  the  deposition  of  peroxide  of  manganese  in  formic  acid 
solution  took  place  more  quickly  when  sodium  formate  was  pres- 
ent, than  without  it,  so  in  this  case  the  complete  precipitation  is 
from  one-half  to  one  hour  slower  without  than  with,  even  as  little 
as  10  drops  or  0.05  gram  of  sodium  sulphite.  Still  without  its 
use  there  is  no  danger  of  any  deleterious  effect  due  to  its  presence, 
and  the  character  of  the  deposit  of  peroxide  shows  a  decided  im- 
provement, it  being  almost  entirely  adherent.  Only  a  trifle  came 
off  during  the  washing  and  this  small  amount  could  easily  be 
collected  on  a  small  filter  and  added  to  the  deposit  in  the  dish. 
The  final  experiments  were  run  in  the  following  manner:  10  cc. 
of  manganese  sulphate  solution  containing  0.0988  gram  of  manga- 
nese were  introduced  into  the  roughened  platinum  dish,  and  10  cc. 
of  ferric  ammonium  sulphate  solution  contaning  0.0996 
of  iron  were  added.  Then  5  cc.  of  formic  acid  of 
1.06  specific  gravity  and  10  cc.  of  an  ammonium  ace- 
tate solution,  obtained  by  neutralizing  1.06  specific  grav- 
ity acetic  acid  by  ordinary  chemically-pure  ammonia  to  barely 
acid  reaction,  were  added,  the  basket  electrode  introduced  and  a 
current  of  1.1  amperes,  with  a  pressure  of  3.9  volts  between  the 
electrodes,  was  allowed  to  act  for  five  hours.  At  the  end  of  this 
time  the  level  of  the  solution  was  raised,  and  no  further  precipita- 
tion took  place.  The  solution  was  then  siphoned  off  as  before, 
both  of  the  electrodes  washed  carefully  and  the  iron  titrated  in  the 
usual  manner,  while  the  manganese  peroxide,  after  the  small 
amount  of  loose  material  had  been  filtered  off  and  added  to  the 
material  in  the  dish,  was  ignited  and  weighed  in  the  usual  manner. 
The  following  table  shows  the  close  agreement  of  the  results 
obtained : 


28 


«j 

I 

0 

1 
0 

s 

f 

V 

1 
I 

■ 

1 

I 

a 
| 

i 

a 
2 

T3 

C 

5 
I 

c 
5 

s 
< 

Formic    t 

sp.gr. 
Time. 
Hours. 

2 

B 

& 

s 

0 

| 
0 
* 

si 

O.O996 

O.0996 

0.0988 

O.0990 

10  cc.  -f  10 
drops  Na^SOs 

5    4 

ordi- 
nary. 

I.I 

1.83 

3.9 

O.O996 

0.0994 

0.0988 

O.0991 

t< 

5    4 

<< 

I.I 

I.83 

3.9 

O.O996 

0.0994 

0.0988 

O.0986 

10  cc,  no 
NajS03. 

5    5 

" 

I.I 

1.83 

3.9 

O.O996 

0.0995 

0.0988 

0.0988 

" 

5    5 

<« 

I.I 

1.83 

3-9 

O.O996 

0.0995 

0.0988 

0.0990 

» 

5    5 

<< 

I.I 

1.83 

3-9 

O.O996 

0.0994 

0.0988 

O.0990 

<< 

5    5 

♦  r 

I.I 

I.83 

39 

The  deposit  of  iron  has  a  shining,  metallic  appearance  and  the 
peroxide  of  manganese  is  obtained  in  a  black,  lustrous  form, 
almost  altogether  adherent  to  the  dish. 

It  is  apparent  from  the  preceding  description,  that  the  results  of 
this  investigation  have  been  very  satisfactory.  It  has  been  proven, 
that  a  complete  separation  of  iron  and  manganese  can  be  effected 
in  a  very  simple  manner  and  the  fact,  that  both  metals  are  obtained 
at  the  same  time,  the  one  as  metal  on  the  kathode  and  the  other  as 
peroxide  on  the  anode,  constitutes  a  considerable  ad  vantage  over  the 
other  methods  proposed  up  to  now  and  described  above.  The 
time  of  deposition,  compared  with  that  necessary  in  Kaeppel's 
method,  has  been  reduced  from  eight  and  one-half  to  nine  and  one- 
half  hours,  which  are  required  to  precipitate  the  iron  alone  by  that 
method,  to  four  or  five  hours,  when  both  metals  are  completely 
precipitated.  There  is  no  floating  matter  of  any  kind  swimming 
in  the  dish  in  which  the  electrolysis  is  carried  out,  and  conse- 
quently no  chance  for  contamination  of  one  or  both  of  the  deposits. 
Furthermore  there  is  no  necessity  of  watching  the  operation,  as 
owing  to  the  low  current  used,  the  electrolyte  does  not  heat  up  and 
the  voltage  and  amperage  remain  constant.  Compared  with  the 
usual  gravimetric  methods  which  demand  considerable  analytical 
skill  and,  especially  in  the  case  of  the  basic  acetate  separation,  con- 
sume a  great  deal  of  time  for  the  filtering  and  washing  of  slimy 
precipitates,  the  electrolytic  method  described  above  has  the  ad- 
vantage that  it  is  easy  of  execution  and  requires  practically  no 
manual  labor  and  attention,  after  the  electrolysis  is  once  started. 

While  the  work  thus  far  described  was  in  progress,  investiga- 


29 

tions  were  also  conducted  with  other  organic  acids,  to  find  out  how 
their  presence  in  the  solution  would  influence  the  deposition  of 
peroxide  of  manganese.  The  acids  tried  were  propionic,  butyric, 
malonic,  succinic,  tartaric,  citric  and  fumaric  acids.  They  were 
used  in  varying  quantities  either  alone  or  in  conjunction 
with  varying  amounts  of  their  ammonium  salts.  The  results, 
however,  were  not  satisfactory  for  it  was  found  that  nearly  all  of 
them  retailed  or  entirely  prevented  the  deposition  of  peroxide  in 
reasonable  time.  Citric  acid  was  quite  extensively  experimented 
with,  in  quantities  from  i  gram  to  18  grams,  as  it  was  hoped  that 
it  might  lend  itself  to  a  separation  of  manganese  from  iron.  Some 
good  results  were  obtained  by  its  use,  but  for  some  reason,  which 
has  not  been  further  investigated,  it  was  impossible  to  obtain  con- 
cordant results.  Sometimes  the  manganese  would  be  out  of  the 
solution  in  three  to  four  hours,  and  in  experiments  run  to  all 
intents  and  purposes  in  the  same  manner  in  order  to  duplicate  the 
results,  it  would  not  be  out  in  seven  or  eight  hours.  It  is  alto- 
gether probable  that  the  peroxide  goes  into  solution  again,  when 
electrolysis  is  continued  too  long.  Citric  acid  was  therefore  finally 
abandoned. 

The  only  one  of  these  acids  which  worked  satisfactorily  was 
fumaric  acid.  The  best  conditions  for  electrolysis  were  found  to 
be  the  following :  10  cc.  of  a  solution  of  manganese  sulphate  were 
introduced  into  the  roughened  platinum  dish,  the  solution  was 
diluted  and  heated  to  50°-6o°  C.  One  gram  of  fumaric  acid  was 
then  added,  the  electrolyte  made  up  to  130  cc,  the  basket  electrode 
was  introduced  and  a  current  of  0.6  to  1.1  amperes  was  allowed  to 
act  for  three  to  three  and  one-half  hours.  The  pressure  between 
the  electrodes  was  4.2  volts.  The  above  temperature  was  main- 
tained during  the  experiment.  The  deposit  obtained  was  not  en- 
tirely adherent,  about  one-sixth  of  it  being  loose.  The  weights  of 
manganese  protosesquioxide  obtained  were  0.1445,  0.1143,  0.1149 
grams  in  three  experiments,  which  agrees  very  closely  with  the 
amount  of  manganese  present. 

The  above  work  was  undertaken  at  the  suggestion  of  Professor 
Edgar  F.  Smith,  to  whom  the  author  is  under  great  obligation  for 
many  kindnesses.  His  constant  interest  in  the  work,  his  kind  ad- 
vice and  many  helpful  suggestions  were  a  never-failing  source  of 
encouragement  and  inspiration.  It  is  therefore  with  great  pleasure 
that  the  author  begs  to  extend  to  him  his  heartiest  thanks. 


lABKAj^ 


